Energy

1. Energy

2. Bellringer • Write your name on a piece of loose leaf paper. • Take out your lab from last year • Pendulum Pun

3. Objectives • Finish the lab • Analyze Your Grade • Race Track Demo

4. Grades • If the quarter ended right now, would you be happy with your grade? • If you’re not, what will you do to change it?

5. Race Track Demo • To the back

6. Bellringer • What is the only variable that changes the period of a pendulum?

7. Objectives • Learn about the different forms of energy and how to use them to solve problems.

8. The Many Forms of Energy • What are some forms of energy that you have heard of before? • We’re going to start be focusing on two types of energy. • The unit of energy is J for Joule

9. Kinetic Energy • What does kinetic mean? (Think about kine-matics, and kinetic friction) • Kinetic Energy is the energy of a moving object. • Every moving object has kinetic energy.

10. Kinetic Energy • If a puck with a mass of 2kg is sliding on frictionless ice at a constant velocity of 5m/s. What is its kinetic energy? • 25J • If an object is accelerating, how is its kinetic energy changing? • Its kinetic energy is increasing

11. Potential Energy • Energy that is stored due to interactions between objects in a system is called potential energy. • Gravitational Potential Energy is the energy stored in an object due to gravity • GPE=mgh

12. Gravitational Potential Energy • How do you store GPE in an object? • To store GPE you simply increase the distance of the object from the reference level. • Reference level: A position that you chose to define the GPE as zero.

13. Reference Level • Where should the reference level be for the roller coaster below?

14. Gravitational Potential Energy • Which has more GPE: a 9lb bowling ball that is 2m above the ground or a 9lb bowling ball that is 4m above the ground? • The bowling ball that is 4m above the ground will have twice as much GPE as the bowling ball 2m above the ground.

15. Transformation of Energy • Money analogy • Pendulum demo

16. Conservation of Energy • The law of conservation of energy states that in a closed, isolated system, energy can neither be created nor destroyed; rather, energy is conserved. • Under these conditions, energy can change form but the system’s total energy in all of its forms remains constant.

17. Conservation of Energy • Total energy • KE = Kinetic energy • PE = Potential energy • Q = Internal energy • Internal energy can be a variety of things. • Explains the loss of energy to friction

18. Conservation of Energy • After an arrow is fired from a bow it has 300J of kinetic energy. If energy was conserved, what was the potential energy stored in the bow before the arrow was shot?

19. Conservation of Energy • Is energy conserved in a pendulum? • If a 6.8kg bowling ball is 1.0m above its lowest point in its swing, what is its maximum velocity? • Draw a diagram.

20. Conservation of Energy • 4.4m/s

21. Conservation of Energy • Race Track Demo • Where should the two marbles land, and why?

22. Conservation of Energy • Pin in Pendulum demo • Is the period of the pendulum the same on both sides? • What evidence shows us that energy is still conserved even though the period is changing?

23. Conservation of Energy • Magic Cleaning Can • Use the law of conservation of energy to explain why the can comes back to me.

24. Conservation of Energy • Dropper Popper • Use the law of conservation of energy to explain how you can predict the how high the popper will jump.

25. Conservation of Energy • Balloons • Use the law of conservation of energy to explain why the balloon flies away when it is released. • Use the law of conservation of momentum to explain why the balloon flies away when it is released.

26. Classwork • Read Chapter 11 for clarification. • One page 312-313 answer the following questions: • 33,37, 40,49,51, 58, 59, & 64.

27. Bellringer • What is the velocity of a pendulum at the bottom of its path if it is released from 2 meters above its lowest point? • v=6.3m/s

28. Objective • Lab # 14 • Introduction to the next part of energy

29. Homework • Energy HW Packet! • Three short homework assignments. • All due Monday 1/13 • Collected • Counts as three homework assignments • Boost your grades!

30. Bellringer • Explain how energy is conserved in a simple pendulum. • https://phet.colorado.edu/en/simulation/energy-skate-park-basics • Skate park energy conservation demo

31. Objectives • Finish Lab 14 and go over the answers to the post lab questions • Investigate springs, and compare them to what we have already learned about pendulums

32. Homework • Please pass up your homework assignments.

33. Midterm • Midterm will be either the last week of January or the first week of February • It will cover all of mechanics • 1-D and 2-DKinematics, Dynamics & Statics, Work & Energy, Momentum and Impulse, Uniform Circular Motion, Newton’s Universal Law of Gravitation, and Measurement & Math

34. Midterm • Two mods long • Multiple Choice and Long Answer • All Regents type questions • “College” Midterm • You will use everything I’ve given you to study. • We won’t review in class for it. • See me if you have questions or need help.

35. Lab 14 • Finish collecting your data then disassemble everything and leave it on your table. • We will answer the post-lab questions together.

36. Bellringer • What variable of a pendulum should you change to maximize its velocity at the bottom of its swing?

37. Objectives • Discover another useful way of continually transforming energy between kinetic and potential energy.

38. Bellringer • Explain how energy is conserved in a simple pendulum. • https://phet.colorado.edu/en/simulation/energy-skate-park-basics • Skate park energy conservation demo

39. Objective • Investigate springs, and compare them to what we have already learned about pendulums

40. Homework • Please pass up your homework assignments.

41. Midterm • Midterm will be either the last week of January or the first week of February • It will cover all of mechanics • 1-D and 2-DKinematics, Dynamics & Statics, Work & Energy, Momentum and Impulse, Uniform Circular Motion, Newton’s Universal Law of Gravitation, and Measurement & Math

42. Midterm • Two mods long • Multiple Choice and Long Answer • All Regents type questions • “College” Midterm • You will use everything I’ve given you to study. • We won’t review in class for it. • See me if you have questions or need help.

43. Pendulums • Are pendulums the only simple system that easily show how energy can be transformed repeatedly between potential and kinetic while being conserved? • NOT A CHANCE!!!!

44. SPRINGS!!!! • Like pendulums, springs can also display periodic motion! • Periodic Motion: Motion that repeats in a regular cycle. • Springs can be used to show Simple Harmonic Motion! • SHM: Any system in which the force acting to restore an object to its equilibrium position is directly proportional to the displacement of the object.

45. Hooke’s Law • Robert Hooke was a British physicist who discovered the simple harmonic motion of springs. • He published his discovery in 1660 in a Latin anagram. • He later published the solution in 1678

46. Hooke’s Law • Hooke’s Law states that a spring exerts a force directly proportional to the distance it is stretched.

47. Hooke’s Law’s Units • The negative sign in Hooke’s Law indicates that the force is in the direction opposite the stretch or compression direction (always towards equilibrium). • The larger the k value, the stiffer the spring.

48. Hooke’s Law Example • What is the force of a spring that has a spring constant of 67N/m and is stretched 0.25m • 16.75N towards equilibrium • What is the spring constant of a spring that is compressed 0.33m away from its equilibrium position with a force of 12N? • 36.4N/m

49. Hooke’s Law is FLAWED!! • Hooke’s law does not work for every spring (i.e. rubber bands). • Springs that obey Hooke’s law are called elastic springs. • The Elastic Limit of a spring • Metal springs usually can only be stretched or compressed so much before they deform.

50. Spring Potential Energy • Springs can also store potential energy • What happens to the potential energy of a spring as you compress or stretch it more and more? • It increases, until it becomes too much and breaks…